1. Field of the Invention
This invention relates to a metal-composite hose used in a fluid pipeline, such as a fuel or refrigerant hose, and a process for manufacturing the same. More particularly, it relates to a metal-composite hose having high fluid impermeability, flexibility and strength, as well as high metal-rust resistance and sealing property at both ends, and a process for the effective manufacture thereof. This invention is particularly favorably applied to a corrugated metal-composite hose. A corrugated hose is a hose having a corrugated wall along at least a part of its length excluding both ends.
2. Description of the Related Art
Various kinds of rubber hoses have usually been used as, for example, fuel hoses of motor vehicles. Rubber hoses are good in vibration absorbability and flexibility for assembly. A new type of rubber hose has recently come to draw attention in view of its fuel impermeability considered important for environmental protection. For example, there is a hose having a wall formed from resin having a higher fuel impermeability than rubber, and bent or corrugated partly for improved vibration absorbability and flexibility.
Further tightening of fuel emission control is, however, expected. It is also necessary to consider measures against a highly permeant fluid, such as a carbon dioxide refrigerant, or hydrogen gas for a fuel cell. It is, therefore, necessary to consider a corrugated metal and resin composite hose having a barrier metal layer expected to provide a very high fluid impermeability and a reinforcing resin layer, and corrugated to ensure flexibility.
A corrugated metal and resin composite hose is disclosed in, for example, JP Kokai No. 275981/1995. It is manufactured by coating the outer surface of a straight metal pipe with a resin layer and corrugating the metal and resin layers together by drawing, hydroforming or the like. Such corrugation, however, permits their deformation only to a limited degree, whether by drawing or by hydroforming. The metal layer is, for example, likely to break unless its elongation is limited to 20% or less. Such a limited deformation does not allow any satisfactory plastic deformation of the resin layer. As a result, the stress produced by the resin layer during the corrugation of the pipe makes it difficult for the metal layer to retain its corrugated shape. Such difficulty may be overcome by forming a relatively thick metal layer and a relatively thin resin layer. The mere formation of a thick metal layer may, however, result in a corrugated hose having a higher cost, a greater weight and a lower flexibility. The mere formation of a thin resin layer may result in a hose which is so low in mechanical strength as to collapse when it is installed.
Another serious problem encountered usually by a metal and resin composite hose is the fatigue failure of its metal layer caused by its repeated vibration and deformation. Such fatigue failure of the metal layer has to be prevented by the effective reinforcement by the resin layer. The inventors of this invention have found that any imbalance in thickness between a metal and a resin layer is likely to cause insufficient reinforcement by the resin layer and the resultant fatigue failure of the metal layer.
JP Kokai No. 127101/1996 discloses a metal and resin composite hose for supplying hot water for cooking, washing or heating, or for discharging waste water. It has a multilayer wall composed of a metal layer, a modified polyolefin layer and a polybutene layer, formed by two cycles of resin powder coating around a metal layer, to give it hot water resistance and prevent its cracking.
The inventors of this invention have proposed a corrugated metal-composite hose and a process for manufacturing the same in JP Kokai No. 341230/2001. The hose is satisfactory in all of fluid impermeability, flexibility for installation and vibration absorbability, and strength to resist collapsing when it is installed. Moreover, its resin layer is effective for reinforcing its metal layer against fatigue failure.
The inventors' further research has, however, revealed the following. Water, such as rainwater, splashed water containing an antifreezing agent, or condensed moisture, may collect at a joint portion (or a sealing portion) at the end of the hose. The conventional metal-composite hose has its metal layer exposed at each end thereof to a sealing portion. Namely, the metal layer at each end serves as a sealing surface against a connecting pipe or the like. Such a hose may have insufficient water seal, and the collected water may corrode the metal layer.